diff --git a/gossipsub.go b/gossipsub.go
index 4ff1da3..9608bec 100644
--- a/gossipsub.go
+++ b/gossipsub.go
@@ -75,6 +75,13 @@ var (
 	// then there is no PRUNE response emitted. This protects against GRAFT floods and should be
 	// less than GossipSubPruneBackoff.
 	GossipSubGraftFloodThreshold = 10 * time.Second
+
+	// Maximum number of messages to include in an IHAVE message. Also controls the maximum
+	// number of IHAVE ids we will accept and request with IWANT from a peer within a heartbeat,
+	// to protect from IHAVE floods. You should adjust this value from the default if your
+	// system is pushing more than 5000 messages in GossipSubHistoryGossip heartbeats; with the
+	// defaults this is 1666 messages/s.
+	GossipSubMaxIHaveLength = 5000
 )
 
 // NewGossipSub returns a new PubSub object using GossipSubRouter as the router.
@@ -87,6 +94,7 @@ func NewGossipSub(ctx context.Context, h host.Host, opts ...Option) (*PubSub, er
 		gossip:  make(map[peer.ID][]*pb.ControlIHave),
 		control: make(map[peer.ID]*pb.ControlMessage),
 		backoff: make(map[string]map[peer.ID]time.Time),
+		iasked:  make(map[peer.ID]int),
 		connect: make(chan connectInfo, GossipSubMaxPendingConnections),
 		mcache:  NewMessageCache(GossipSubHistoryGossip, GossipSubHistoryLength),
 	}
@@ -203,6 +211,7 @@ type GossipSubRouter struct {
 	lastpub map[string]int64                 // last publish time for fanout topics
 	gossip  map[peer.ID][]*pb.ControlIHave   // pending gossip
 	control map[peer.ID]*pb.ControlMessage   // pending control messages
+	iasked  map[peer.ID]int                  // messages we have asked for in the last heartbeat
 	backoff map[string]map[peer.ID]time.Time // prune backoff
 	connect chan connectInfo                 // px connection requests
 	mcache  *MessageCache
@@ -364,6 +373,12 @@ func (gs *GossipSubRouter) handleIHave(p peer.ID, ctl *pb.ControlMessage) []*pb.
 		return nil
 	}
 
+	// IHAVE flood protection
+	if gs.iasked[p] >= GossipSubMaxIHaveLength {
+		log.Debugf("IHAVE: peer %s has already advertised too many messages; ignoring", p)
+		return nil
+	}
+
 	iwant := make(map[string]struct{})
 	for _, ihave := range ctl.GetIhave() {
 		topic := ihave.GetTopicID()
@@ -384,7 +399,12 @@ func (gs *GossipSubRouter) handleIHave(p peer.ID, ctl *pb.ControlMessage) []*pb.
 		return nil
 	}
 
-	log.Debugf("IHAVE: Asking for %d messages from %s", len(iwant), p)
+	iask := len(iwant)
+	if iask+gs.iasked[p] > GossipSubMaxIHaveLength {
+		iask = GossipSubMaxIHaveLength - gs.iasked[p]
+	}
+
+	log.Debugf("IHAVE: Asking for %d messages from %s", iask, p)
 
 	iwantlst := make([]string, 0, len(iwant))
 	for mid := range iwant {
@@ -394,6 +414,10 @@ func (gs *GossipSubRouter) handleIHave(p peer.ID, ctl *pb.ControlMessage) []*pb.
 	// ask in random order
 	shuffleStrings(iwantlst)
 
+	// truncate to the messages we are actually asking for and update the iasked counter
+	iwantlst = iwantlst[:iask]
+	gs.iasked[p] += iask
+
 	return []*pb.ControlIWant{&pb.ControlIWant{MessageIDs: iwantlst}}
 }
 
@@ -867,6 +891,9 @@ func (gs *GossipSubRouter) heartbeat() {
 	// clean up expired backoffs
 	gs.clearBackoff()
 
+	// clean up iasked counters
+	gs.clearIasked()
+
 	// ensure direct peers are connected
 	gs.directConnect()
 
@@ -1039,6 +1066,13 @@ func (gs *GossipSubRouter) heartbeat() {
 	gs.mcache.Shift()
 }
 
+func (gs *GossipSubRouter) clearIasked() {
+	if len(gs.iasked) > 0 {
+		// throw away the old map and make a new one
+		gs.iasked = make(map[peer.ID]int)
+	}
+}
+
 func (gs *GossipSubRouter) clearBackoff() {
 	// we only clear once every 15 ticks to avoid iterating over the map(s) too much
 	if gs.heartbeatTicks%15 != 0 {
@@ -1123,6 +1157,15 @@ func (gs *GossipSubRouter) emitGossip(topic string, exclude map[peer.ID]struct{}
 		return
 	}
 
+	// shuffle to emit in random order
+	shuffleStrings(mids)
+
+	// if we are emitting more than GossipSubMaxIHaveLength mids, truncate the list
+	if len(mids) > GossipSubMaxIHaveLength {
+		log.Debugf("too many messages for gossip; truncating IHAVE list (%d messages)", len(mids))
+		mids = mids[:GossipSubMaxIHaveLength]
+	}
+
 	// Send gossip to GossipFactor peers above threshold, with a minimum of D_lazy.
 	// First we collect the peers above gossipThreshold that are not in the exclude set
 	// and then randomly select from that set.